We request a Becton-Dickinson FACS IV fluorescence activated cell sorter to serve the needs of core and peripheral users distributed in several departments on the Columbia University main campus and the medical school. The novel feature of the particular facility requested is the capability for multiple wavelength and UV excitation which will allow the development and use of cell sorting and analysis based on fluorescence energy transfer, excimer formation, and differential quenching. The novel features of the user population are groups of both fluorescence spectroscopists and cell biologists. The need for this instrument is justified by two considerations: the lack of any multiwavelength multiparameter FACS at Columbia, and the large number of ongoing research projects which now require such a capability.